Process for forming a semifluid grease involving cooling to a subzero temperature



United States Patent PROCESS FOR FORMING 'A SEMIFLUID GREASE INVOLVINGCOOLING TO A SUBZERO TEM- PERATURE Kurt R. Fisch, Philadelphia, Pa.,assignor to the United States of America as represented by the Secretaryof the Army No Drawing. Filed Dec. 18, 1957, Ser. No. 703,710

3 Claims. (or. 252- 333) (Granted under Title 35, US. Code (1952), sec.266) The invention described herein may be manufactured and used by orfor the Government for governmental purpose without the payment of anyroyalty thereon.

This invention relates to a semifluid grease composition for use as anextreme pressure lubricant and to a method for its preparation.

An important object of this invention is to provide a lubricatingcompound for the rotating and elevating mechanisms of a gun able towithstand (extremely high) pressures of the order of 60,000 p.s.i.,thought to be from gases escaping from the gun, without decomposing orevaporating.

Another object of this invention is to provide a composition whichretains its lubricating properties when subjected to severe cold workingconditions.

With the advent of modern firearms capable of firing at rapid speedscausing pressures to mount to 57,000 lbs. per square inch andtemperatures to reach well above 260 F., the problem of properlubrication of these mechanisms became very acute. The lubricants knownto the prior art were inadequate in that they either broke down orevaporated at the extremely high pressures, or else when subjected to atemperature well below the freezing point of water, they gelled andbecame very stiff.

The lubricant made in accordance with this invention has an advantageover the prior lubricants in that it is stable at temperatures of 260 F.and pressures of 60,000 lbs. per square inch, furthermore, when thefiring mechanisms are subjected to temperatures as low as -65 F.,permitting satisfactory operation of the gun.

The invention consists of mixing 80-89% by weight of at least onematerial from a group consisting of esters of adipic, pimelic, suberic,azelaic, sebacic acids, a particularly preferred ester being di-2-ethylhexyl sebacate, having a centistoke viscosity at 100 F. in the rangefrom nine to fourteen and a centistoke viscosity at 65 F. of not morethan 12 thousand with about 1.5 by weight of any rust inhibitor, such asbarium petroleum sulfonate, 1.0% by weight of di isopropyl acidphosphite to enhance extreme pressure stability, about 0.5% of anyoxidation inhibitor from the group having a phenolic derivation, such as2,6-di-tertiary butyl para cresol, to preclude any reaction with the diisopropyl acid phosphite, and from 17.0% to 8% of a thickening agentsuch as lithium stearate. The weight of the thickening agent iscontrolled by the polarity of the other components. The higher theirpolarity the more thickening agent will have to be added to insurestability of the suspension which is formed. The suspension of lithiumstearate is homogeneously dispersed throughout the mixture. The mixtureis heated to 185 C. to 195 C. The temperature must be kept below 195 C.to prevent the formation of a grease which results if the heating isprolonged or if the temperature is too high. The character of thesolution changes above 195 C. resulting in a different crystallinestructure. If

2,991,241. Patented Ju i/4i 1961 2 the temperature is below 185 C. aslurry will result. it has been found empirically that the proper fiberstructure is obtained by keeping the temperature within the prescribedrange.

The mixture is rapidly chilled at a rate of 25 C./minute to a finaltemperature about 30 C. This cooling rate is important to obtain theproper fiber structure. If the rate is any slower by a substantialamount a slurry will result. Proper chilling produces a thixotropicmixture which when worked changes its viscosity and flow characteristicsand becomes a semifluid grease. The resulting compound is then worked ina grease worker to give it the proper mechanical treatment. The size andshape of the fibers in which the liquid is enclosed will determine theproperties of the final composition. After the semifluid grease has beenthoroughly worked by 100 strokes of a grease worker, it is placed in avacuum of about 2 mm. pressure. The air bubbles are then exhausted fromthe composition in a period of two hours.

A specific example which has proved successful within the pressure andtemperature requirements has been pro duced in the following manner:Mixing 89% by weight of di-Z-ethyl hexyl sebacate with 1.5% bariumpetroleum sulfonate, 1% di-isopropyl acid phosphite, and 0.5 2,6-di-tertiary butyl para cresol; adding 8% lithium stearate; homogeneouslydispersing the lithium stearate throughout the mixture; heating themixture to a temperature range from 185 C. to 195 C.; immediatelychilling the mixture at a rate of 25 C./rninute to a final temperatureof -30 C.; homogenizing the mixture and exhausting the air from themixture. Other examples which have been successfully tested have beenproduced by substituting iso amyl adipate and di-Z-ethyl hexyl azelatefor di-2- ethyl hexyl sebacate.

I claim:

1. A method for producing an extreme pressure semifluid greaselubricating composition capable of use at temperatures between about 300F. to -76 F. comprising the steps of forming a mixture of 80 to 89% byweight of an ester selected from the group consisting of esters ofadipic, pimelic, suberic, azelaic and sebacic acids having a centistokeviscosity at F. in the range of 10 to 14 and below about 12,000 at -65F., about 1% by weight of di-isopropyl acid phosphite for impartingextreme pressure stability to said composition, about 1.5% by weight ofbarium petroleum sulfonate for imparting rust inhibiting properties tosaid composition and about 0.5% by weight of 2,6-di-tertiary butyl paracresol for imparting oxidation inhibiting properties to saidcomposition, admixing a thickening agent to said mixture within therange of about 8 to 17% by weight, homogeneously dispersing thethickening agent throughout the mixture, heating the mixture to aboutl95 C. to prevent the thickened mixture fromforming a grease,immediately chilling the heated mixture to about 30 C. at a rateapproximating 25 C. per minute to prevent slurry formation and yetresulting in a thixotropic mixture, and mechanically working thethixotropic mixture to form a semifluid grease.

2. The process of claim 1 wherein said thickening agent is lithiumstearate.

3. The process of claim 1 including the step of exhausting the air fromthe mechanically worked semifluid grease to inhibit separation ofcomponents therefrom.

(References on following page) References Cited in the file of thispatent UNITED STATES PATENTS Bergstrom et a1 J an. 20, 1942 RickettsSept. 1, 1942 Wasson et a1 Mar. 11, 1947 Zisman et a1 Sept. 7, 1948Ashburn et a1 Sept. 28, 1948 Bondi Oct. 31, 1950 Davies et a1. Sept. 4,1951 Eckert Sept. 16, 1952 '4 OTHER REFERENCES Development of SchematicAnalytical Procedures for Synthetic Lubricants and Their Additives,Schmidt et al., WADC Technical Report 54-464, Denver Research Inst.,April 1955, pages 6 and 7.

Manufacture and Application of Lubricating Greases, Boner, Reinhold Pub.Corp., N.Y., 1954, pages 227, 228, 278 and 279.

Concise Chemical and Technical Dictionary, Bennett, Chemical Pub. 00.,N.Y., 1947, page 363.

1. A METHOD FOR PRODUCING AN EXTREME PRESSURE SEMIFLUID GREASELUBRICATING COMPOSITION CAPABLE OF USE AT TEMPERATURES BETWEEN ABOUT300*F. TO -76*F. COMPRISING THE STEPS OF FORMING A MIXTURE OF 80 TO 89%BY WEIGHT OF AN ESTER SELECTED FROM THE GROUP CONSISTING OF ESTERS OFADIPIC, PIMELIC, SUBERIC, AZELAIC AND SEBACIC ACIDS HAVING A CENTISTOKEVISCOSITY AT 100*F. IN THE RANGE OF 10 TO 14 AND BELOW ABOUT 12,000 AT-65*F., ABOUT 1% BY WEIGHT OF DI-ISOPROPYL ACID PHOSPHITE FOR IMPARTINGEXTREME PRESSURE STABILITY TO SAID COMPOSITION, ABOUT 1.5% BY WEIGHT OFBARIUM PETROLEUM SULFONATE FOR IMPARTING RUST INHIBITING PROPERTIES TOSAID COMPOSITION ABOUT 0.5% BY WEIGHT OF 2,6-DI-TERTIARY BUTYL PARACRESOL FOR IMPARTING OXIDATION INHIBITING PROPERTIES TO SAIDCOMPOSITION, ADMIXING A THICKENING AGENT TO SAID MIXTURE WITHIN THERANGE OF ABOUT 8 TO 17% BY WEIGHT, HOMOGENEOUSLY DISPERSING THETHICKENING AGENT THROUGHOUT THE MIXTURE, HEATING THE MIXTURE TO ABOUT185-195*C. AT A RATE APPROXIMATING MIXTURE FROM FORMING A GREASE,IMMEDIATELY CHILING THE HEATED MIXTURE TO ABOUT -30*C. AT A RATEAPPROXIMATING 25*C. PER MINUTE TO PREVENT SLURRY FORMATION AND YETRESULTING IN A THIXOTROPIC MIXTURE, AND MECHANICALLY WORKING THETHIXOTROPIC MIXTURE TO FORM A SEMIFLUID GREASE.